The invention concerns a filter element comprising a filter material, wherein the filter material can be flowed through from a raw side to a clean side by a medium to be filtered. The invention concerns moreover a filter as well as a filter system.
It is known to employ filters for filtering a medium, in particular for filtration of a liquid.
For example, EP 1 648 583 B1 discloses an oil filter. The oil filter comprises a filter element with an overflow valve. When the pressure is too high in the inlet, overflow or bypassing of a filter material of the filter element occurs in the known oil filter. In this context, the overflow valve opens in order to enable direct flow of the oil from the raw side to the clean side of the filter.
When filters are used outdoors, in particular in a motor vehicle, a great change of the outdoor temperature may cause a volume change of the medium, in particular freezing of the medium in the form of a liquid when the outdoor temperature drops. The volume change can lead to the filter becoming damaged.
In order to avoid such a filter damage, it is disclosed in DE 10 2012 017 140 A1 to employ a compensation element in the filter which compensates the volume change of the medium in the filter. Such a compensation element requires however a relatively large installation space in the filter.
Therefore, a compensation element is often not employed in filters and the medium after completion of filtration is pumped out of the filter in order to avoid damage to the filter by temperature changes. In particular, as mentioned before, damage to the filter by a medium freezing in the filter is to be avoided.
Pumping out the medium has however the disadvantage that dirt particles in the filter material become detached and are also pumped out. This can cause damage to the pump or to the throttles, valves, and the like.